The creek on my rural property was a mixture of running water, frozen and freezing ice.
The darker areas had water touching the ice underneath.
Air filled the light areas.
I’m sure the explanation for these shapes would be too complicated for an artistic mind.
The sequence of next 6 pictures was taken in two minutes.
The light areas were light because air filled the void below the ice.
The whole surface was frozen. Air would rush under the ice in spidering directions.
First here and then there. Obviously, the water level was slowly dropping.
Sometimes small areas turned white; other times much larger areas.
This whole area was about three feet square.
The arrow shows where the original opening was.
The word amazing came to mine.